Data Binding and Data Grid View Classes

A PRESENTATION BY

Arvind Krishnaa J

DATA BINDING AND DATA GRID VIEW CLASS

OVERVIEW

• SIMPLE AND COMPLEX DATA BINDING

• ONE-WAY AND TWO-WAY DATA BINDING

• Binding and BindingManagerBase classes

• Sample Data Binding Application

• DataGridView class

DATA BINDING

Link the contents of a control with an underlying data source

WHY DATA BINDING?

• Changes to the immediate data source can be reflected automatically in data controls

bound to it

• Changes in the data control are posted automatically to the intermediate data

source

INTERMEDIATE DATA SOURCE

The term intermediate data source is used to distinguish it from the original data source, which may be an external database

IMPORTANT NOTE

The controls cannot be bound directly to a data source over an active connection.

Binding is restricted to the in-memory representation of the data.

MULTIPLE CONTROLS BOUND TO A SINGLE DATA SOURCE

SIMPLE DATA BINDING

Simple data binding, which is available to all controls, links a data source to one or more properties of a control.

DATA BINDING WITH A TEXTBOX

An application can set properties of a textbox dynamically by binding them to a data source.

The following program creates an object whose public properties are mapped to the properties on the TextBox

Simple data binding code

// Create object (width, text, color)

TextParms tp = new TextParms(200, "Casablanca", Color.Beige);

Method 1:

// Bind text and BackColor properties of control

txtMovie.DataBindings.Add("Text", tp, "Tb_Text");

txtMovie.DataBindings.Add("BackColor", tp, "Tb_Background");

Method 2:

Binding binding = new Binding("Width", tp, "Tb_Width");

txtMovie.DataBindings.Add(binding);

Where the class TextParams is…

public class TextParams { private int Tb_Width; private string Tb_Text; private Color Tb_Color; public TextParams(int width, string text, Color color) { Tb_Width = width; Tb_Text = text; Tb_Color = color; } }; //with corresponding get and set method for the properties accessing each data member

DATA BINDING ADD METHOD

The DataBindings.Add method creates a collection of bindings that links the data source to the control's properties.

SYNTAX

DataBindings.Add( control property, data source, data member)

control property Property on the control that is being bound.

data source Object that contains data being bound to control.

data member Data member on the data source that is being used. Set this to null if the data source's ToString() method provides the value.

MULTIPLE BINDINGS

A control may have multiple bindings associated with it, but only one per property.

This means that the code used to create a binding can be executed only once; a second attempt would generate an exception.

Multiple Bindings

To avoid this, each call to add a binding should be preceded with code that checks to see if a binding already exists; if there is a binding, it should be removed. if (txtMovie.DataBindings["Text"] != null) txtMovie.DataBindings.Remove(txtMovie.DataBindings["Text"]); txtMovie.DataBindings.Add("Text", tp, "Tb_Text");

BINDING TO A LIST

Instead of binding to a single object, the control can be bound to an array.

The control can still only display a single

movie title at a time, but we can scroll

through the array and display a different title that corresponds to the current array item selected.

USING THE BINDING MANAGER

The simple part

// ArrayList of TextParms objects

ArrayList tbList = new ArrayList();

tbList.Add(new TextParms(200,"Casablanca",Color.Beige));

tbList.Add(new TextParms(200, "Citizen Kane", Color.White));

tbList.Add(new TextParms(200, "King Kong", Color.White));

// Bind to properties on the Textbox

txtMovie.DataBindings.Add("Text", tbList, "Tb_Text");

txtMovie.DataBindings.Add("BackColor", tbList, "Tb_Background");

txtMovie.DataBindings.Add("Width", tbList, "Tb_Width");

SIMPLE BINDING WITH ADO .NET

Binding to a table in a DataSet is basically the same as binding to a list.

For example, the Text property of the control is bound to the movie_Year column in a DataTable.

Binding to a DataSet

ds = new DataSet("films");

string sql = "select * from movies order by movie_Year";

da = new SqlDataAdapter(sql, conn);

da.Fill(ds,"movies"); // create datatable "movies"

// Bind text property to movie_Year column in movies table

txtYr.DataBindings.Add("Text", ds,"movies.movie_Year");

NOTE…

Although the control could be bound directly to a DataTable, the recommended approach is to bind the property to a DataSet and use the DataTable name as a qualifier to specify the column that provides the data.

This makes it clear which table the value is coming from.

COMPLEX DATA BINDING WITH LIST CONTROLS Complex binding is only available on controls that include properties to specify a data source and data members on the data source.

This select group of controls is limited to the ListBox, CheckedListBox, ComboBox, DataGrid, and DataGridView.

ListBox bound to a DataSet

da.Fill(ds,"movies");

DataTable dt = ds.Tables[0];

// Minimum properties to bind listbox to a DataTable

listBox1.DataSource = ds;

listBox1.DisplayMember = "movies.movie_Title";

SOME FINER DETAILS… • After these values are set, the list box is

automatically filled.

• The DataSource property can be changed programmatically to fill the control with a different set of data

• Can be set to null to clear the control's content.

• Although no Binding object is explicitly created, a DataBindings collection is created underneath and is accessible through code.

GROUPING WITH OTHER CONTROLS

Bound list box control is often grouped with other controls, such as a text box or label, in order to display multiple values from a row of data. When the controls are bound to the same data source, scrolling through the list box causes each control to display a value from the same data row.

An example…

txtStudio.DataBindings.Add("Text", ds,"movies.studio");

txtYear.DataBindings.Add("Text", ds,"movies.movie_Year");

ONE-WAY AND TWO-WAY DATA BINDING Data bound to a control can be changed in two ways:

• By updating the underlying data source

• By modifying the visible contents of the control.

Changes should be reflected in the associated control or data in both cases.

This is called TWO-WAY Binding.

ONE-WAY BINDING

A control may be bound to a data source in read-only mode when its only purpose is to present data.

The data-source must be “write-protected”

Updating a Control Value

In the case where a control is bound to a property on an object, the property must provide write support in order for its value to be updated.

public int Movie_Year

{

set

{

myYear = value;

}

get

{

return myYear;

}

}

// Read only property. Control cannot update this.

public string Studio { get { return myStudio; } }

Updating a property If a control is bound to an object property, a change to the value of that property is not automatically sent to the control.

Instead, the binding manager looks for an event named propertyChanged on the data source

// Event to notify bound control that value has changed

public event EventHandler Movie_YearChanged;

// Property control is bound to year value

public int Movie_Year {

set {

myYear = value;

// Notify bound control(s) of change

if (Movie_YearChanged != null)

Movie_YearChanged(this, EventArgs.Empty);

}

get { return myYear; }

}

ADDING OR DELETING AN ITEM FROM THE DATA SOURCE

Controls that are bound to the source using simple binding are updated automatically; controls using complex binding are not.

In the latter case, the update can be forced by executing the Refresh method of a CurrencyManager object

USING BINDING MANAGERS • Each data source has a binding manager that keeps track

of all connections to it.

• When the data source is updated, the binding manager is responsible for synchronizing the values in all controls bound to the data.

• Conversely, if a value is changed on one of the bound controls, the manager updates the source data accordingly. A binding manager is associated with only one data source.

• If an application has controls bound to multiple data sources, each will have its own manager.

BINDING MANAGERS SYNCHRONIZE THE DATA SOURCE AND CONTROLS

COORDINATING THE TWO-WAY FLOW OF DATA BETWEEN A DATA SOURCE AND CONTROL

• Binding

// Create a binding manager object

BindingManagerBase mgr= binding.BindingManagerBase;

• CurrencyManager

• Bindings

• Count

• Current

• Position

• PositionChanged

• CurrentChanged

COORDINATING THE TWO-WAY FLOW OF DATA BETWEEN A DATA SOURCE AND CONTROL

• PropertyManager : This class, which also derives from BindingManagerBase, maps the properties on an object to properties on a bound control.

• BindingContext : A program's main interest in the BindingContext is to use it to gain access to the binding manager for a data source.

BindingManagerBase mgr = this.BindingContext[ds,"movies"]; // Or use casting to get specific manager. CurrencyManager mgr= (CurrencyManager) this.BindingContext[ds,"movies"];

Using the BindingManagerBase to Navigate a list

// Bind listbox to a dataset.datatable

listBox1.DataSource = ds;

listBox1.DisplayMember = "movies.movie_Title";

// Bind to TextBox

txtStudio.DataBindings.Add("text", ds, "movies.studio");

// BindingManagerBase bmb has class-wide scope

bmb = this.BindingContext[ds, "movies"];

// Create delegate pointing to event handler

bmb.PositionChanged += new EventHandler(bmb_PositionChanged);

USING THE POSITIONCHANGED EVENT

The PositionChanged event is fired each time the binding manager moves to a new position in the list.

This could be triggered programmatically or by the user clicking a row in the list box control.

PositionChanged Event

private void bmb_PositionChanged(object sender,EventArgs e)

{

BindingManagerBase bmb = (BindingManagerBase)sender;

// Item should be a DataRowView if from a table

object ob = bmb.Current.GetType();

if (ob == typeof(System.Data.DataRowView))

{

DataRowView view = (DataRowView)bmb.Current;

// Could access: ((string)view["movie_Title"]);

}

}

A sample application . . .

THE DATAGRIDVIEW CLASS

WHAT IS IT?

With more than a hundred properties and methods, the DataGridView is by far the most complex Windows Forms control for displaying data.

KEY FEATURES

• Data binding is supported by the DataSource property.

• DataGridView provides a unique virtual mode that permits it to handle more than 100,000 rows of data.

• DataGridView methods, events, and properties allow an application to easily manage the mapping between virtual and physical storage.

PROPERTIES

• Elegantly simple structure

• Consists of column headers, row headers and cells

• To these, we can add the Columns and Rows collections that allow an application to access the grid by indexing a row or column

BASIC DATAGRIDVIEW ELEMENTS

5 ELEMENTARY STEPS

1. Define column headers

2. Define style for data cells

3. Define style for column headers

4. Define user capabilities

5. Place data in grid (manually or using datasource)

DATABINDING WITH A DATAGRIDVIEW

• A DataGridView is bound to a data source using complex binding

• A DataGridView must display multiple data values

• DataMember property is set to the name of a table within the data source

USING A DATA SOURCE

// Turn this off so column names do not come from data source dataGridView1.AutoGenerateColumns = false;

// Specify table as data source dataGridView1.DataSource = ds; // Dataset dataGridView1.DataMember = "movies"; // Table in dataset // Tie the columns in the grid to column names in the data table dataGridView1.Columns[0].DataPropertyName = “movie_title"; dataGridView1.Columns[1].DataPropertyName = “movie_year"; dataGridView1.Columns[2].DataPropertyName = “studio";

AND ANOTHER SAMPLE APPLICATION . . .

OTHER INTERESTING PROPERTIES

• Frozen Columns

• ReadOnly Columns

• Minimum Width

• Sorting

• Multiple Column Types : Six predefined column classes are available that can be used to represent information in a grid, : TextBox, CheckBox, Image, Button, ComboBox, and Link. The name for each of these controls follows the format DataGridViewControlnameColumn.

EXAMPLE

DataGridViewButtonCell aButton = new DataGridViewButtonCell ();

and similarly for other 5 controls.

EVENTS

Just about every mouse and cursor movement that can occur over a DataGridView can be detected by one of its events

Cell actions

CellValueChanged (1) Occurs when the value of a cell changes.

CurrentCellChanged (3) Occurs when the value of the current cell changes

CellClick (1) Occurs when any part of the cell is clicked. This includes cell borders and padding.

CellContentClick (1) Occurs only if the cell content is clicked.

CellEnter (1) CellLeave (1)

Occurs when cell receives/loses input focus.

CellFormatting (5) Occurs prior to formatting a cell for display.

CellMouseClick (2) CellMouseDoubleClick (2)

Occurs whenever a mouse clicks/double clicks anywhere on a cell.

CellMouseDown (2) CellMouseUp (2)

Occurs when a mouse button is pressed/raised while it is over a cell

CellMouseEnter (1) CellMouseLeave (1)

Occurs when the mouse pointer enters or leaves a cell's area.

CellPainting (6) Raised when a cell is to be painted.

Column actions ColumnHeaderMouseClick (2) ColumnHeaderMouseDouble-Click (2)

Occurs when a column header is clicked/double clicked.

Row actions RowEnter (1) RowLeave (1)

Occurs when a row receives/loses the input focus.

RowHeaderMouseClick (2) RowHeaderDoubleMouse-Click (2)

Occurs when a user clicks/double clicks a row header

UserAddedRow (4) UserDeletedRow (4)

Occurs when a user adds/deletes a row in the grid.

Data error DataError (7) Occurs when an external data parsing or validation operations fails. Typically occurs due to an attempt to load invalid data into a data grid cell.

Associated Delegates (1) public sealed delegate void DataGridViewCellEventHandler(object sender, DataGridViewCellEventArgs e)

(2) public sealed delegate void DataGridViewCellM_useEventHandler(object sender, DataGridViewCellMouseEventArgs e)

(3) public sealed delegate void EventHandler(object sender, EventHandlerArgs e) (4) public sealed delegate void DataGridViewRowEventHandler(object sender, DataGridViewRowEventArgs e) (5) public sealed delegate void DataGridViewCellFormattingEventHandler(object sender, DataGridViewCellFormattingEventArgs e) (6) public sealed delegate void DataGridViewCellPaintingEventHandler(object sender, DataGridViewCellPaintingEventArgs e) (7) public sealed delegate voidDataGridViewDataErrorEventHandler(object sender, DataGridViewDataErrorEventArgs e)

SOME IMPORTANT EVENTS

1. Cell Formatting : The CellFormatting event gives you the opportunity to format a cell before it is rendered. This comes in handy if you want to distinguish a subset of cells by some criteria.

2. Recognizing Selected Rows, Columns, and Cells

3. Data Error Handling : The DataError event fires when a problem occurs loading data into a grid or posting data from the grid to the underlying data store.

MASTER-DETAIL DATAGRIDVIEWS Records in the master table have multiple associated records in the detail table

MASTER-DETAIL DATAGRIDVIEWS

• The master grid is bound to the movies table

• Details grid is bound to the actors table.

• Both tables, as shown, contain the columns that are bound to their respective DataGridView columns.

• In addition, they contain a movieID column that links the two in the master-detail relationship.

NEED FOR VIRTUAL MODE

• When a DataGridView is bound to a data source, the entire data source must exist in memoryDetails grid is bound to the actors table.

Enables quick refresh of control’s cells

Х Large data store may have prohibitive memory requirements.

VIRTUAL MODE

• To handle excessive memory requirements, a DataGridView can be run in virtual mode by setting its VirtualMode property to True.

• In this mode, the application takes responsibility for maintaining an underlying data cache to handle the population, editing, and deletion of DataGridView cells based on actions of the user.

• The cache contains data for a selected portion of the grid

SO WHAT’S COOL?

If a row in the grid cannot be satisfied from cache, the application must load the cache with the necessary data from the original data source

DATA BINDING VERSUS VIRTUAL MODE

VIRTUAL MODE EVENTS

These events are triggered only in virtual mode.

Event Description

NewRowsNeeded Virtual mode event. Occurs when a row is appended to the DataGridView.

CellValueNeeded Virtual mode event. Occurs when cell in grid needs to be displayed.

CellValuePushed Virtual mode event. Occurs when a cell value is edited by the user.

RowValidated Occurs when another row is selected.

UserDeletingRow Occurs when a row is selected and the Delete key is pressed.

TRIGGERED EVENT HANDLERS

• RowNeeded : Is triggered when the user begins to add a new row at the bottom of the grid. currRow is set to the row number of any row being added.

• CellNeeded : Is triggered when a cell needs to be redrawn. This does not require that a row be selected, but occurs as you move the cursor over cells in the grid. This routine identifies the column the cell is in and displays the data from the cache or the object that is created for new rows. Note that the MapRow() is called to translate a row in the grid to its corresponding row in the cache. In this simple example, there is always a one-to-one relationship because the cache and grid contain the same number of rows. In a production application, row 5000 in a grid might map to row 1 in the cache.

TRIGGERED EVENT HANDLERS(CONTD…)

• CellPushed : Called when a cell value is edited. This routine updates a movie object that represents the selected row with the new value.

• RowValidated : Signals that a different row has been selected and is used to update the previous row. If the row exists in the cache, it is updated; a new row is added to the cache.

• RowDeleting : Called when user selects a row to delete. If the row exists in the cache, it is removed.

THANK YOU FOR YOUR PATIENCE

Slides Prepared and presented by : ARVIND KRISHNAA J